Printing by means of the resistive ribbon thermal transfer technique is a desirable method of printing, having a number of advantages. In printing by resistive ribbon thermal transfer, an electrically resistive ribbon is pattern-wise heated by the passage of current through the ribbon. The operation of pattern-wise heating the ribbon melts neighboring regions of a layer of ink that forms one surface of the ribbon and renders it pattern-wise transferable while contacting the ink surface of the ribbon to the paper to be printed.
A resistive ribbon thermal transfer printing ribbon (also referred to herein as the "thermal transfer ribbon" or simply "ribbon") useful in such processes typically comprises three layers, viz.:
(1) a resistive film of polymeric material, such as a polycarbonate, containing conductive carbon particles; PA0 (2) a thin metal layer, e.g., an evaporated aluminum film deposited upon the resistive film having a thickness of about 1,000 A, and PA0 (3) a fusible ink layer formed, e.g., from a polymeric material and carbon black. PA0 (1) positioning a used resistive ribbon thermal transfer printing ribbon in a colloidal dispersion of an electrophoretically depositable ink prepared by PA0 (2) passing an electric current through said colloidal dispersion, with an electrically conductive layer of said ribbon serving as one electrode, to electrophoretically deposit the pigment-containing polymeric colloid on areas of said ribbon that have been depleted of ink, to form an ink layer of uniform thickness.
Layer (2) may be omitted, but is preferred to achieve improved resolution.
When such a resistive thermal transfer ribbon is used for printing, the ink is transferred from the heated spots and transferred to the surface being printed. Due to the depletion of ink corresponding to the printed patterns made thereby, the ribbon can not be reused unless a uniform coating of a fusible ink is again formed on the surface of the ribbon. Processes for depositing a uniform thickness of ink over all regions of the ribbon would not be expected to be useful for such reinking, as the resulting ribbon would not have a uniform thickness of ink thereon.
A number of processes have been described in the prior art for reconditioning, e.g., typewriter ribbons. U.S. Pat. No. 2,051,942, issued Aug. 25, 1936 describes the total reinking of used typewriter ribbons with a composition based on coconut oil, and including also sulfuric acid, lamp black, and gum arabic; the composition is applied to the face of the used typewriter ribbon, and after allowing time for penetration into the pores of the typewriter ribbon, excess composition is removed, e.g., by scraping, from the face of the ribbon.
U.S. Pat. No. 2,155,653, issued Apr. 25, 1939, describes a method for redistributing ink from undepleted areas of a typewriter ribbon to the depleted areas to form a uniformly inked ribbon by means of treatment with hydrocarbon vapors. Of course this process could be used only a limited number of times because as the density of the redistributed ink becomes lower it would adversely affect the quality of the typed images formed using such a ribbon.
U.S. Pat. No. 3,105,769, issued Oct. 1, 1963, describes a liquid solution intended to soften and redistribute pigment remaining in a used typewriter ribbon (and the like) and to distribute "body" material included in the solution to the ribbon by means of capillary action.
Processes for coating small electrically conductive articles by electric deposition are known in the art, such as the process described in U.S. Pat. No. 3,539,489, issued Nov. 10, 1970.